Field of the Invention
The present invention pertains to the field of steelmaking. More particularly, the present invention pertains to an improved method of using an improved skimmer paddle for separating slag from a quantity of desired molten metal during the steelmaking process.
Background Art
The present invention relates to the removal of slag from the surface of a quantity of molten metal after the metal has been treated in a ladle. Efficient removal of slag reduces production costs, and improves yield and steel quality. Slag is a waste product formed during the steelmaking process that separates and floats to the surface of the molten metal, where it can be removed by skimming the surface of the molten metal, to scrape the slag off into a slag pot or other waste collection container. Under normal circumstances, when skimming, a small portion of the slag will be inaccessible to the skimmer paddle and scattered along the surface of the molten metal. Consequently the remaining slag will be very difficult to remove. The most popular method for moving the slag into a position where it can be skimmed from the ladle is by installing a bubbling system. Typically, the bubbling system consists of a motor driven “bubbler”, a refractory encased pipe “bubbling lance” (i.e. a pipe encased in a heat-resistant material) inserted into the hot metal in the back portion of the ladle. The refractory coating on the bubbler pipe keeps the pipe from melting due to the temperature of the hot metal. Gas is injected through the pipe and into the hot metal causing turbulence, which tends to push the remaining slag away from the back of the ladle and gather into a position where the skimming paddle can reach it. At this point the skimmer paddle, a hoe-type apparatus, can reach the re-positioned slag and skim it off of the surface of the hot metal and into the slag pot.
The prior art describes an apparatus for efficient slag removal using a paddle and a separate bubbling system in U.S. Pat. No. 5,360,204 (Mancuso). While highly effective, the Mancuso bubbling system requires a motorized hoist to raise and lower the pipe as well as the devices required to start and stop gas flow. The hoist arm in particular is expensive and many steelmakers balk at the extra cost of this permanent equipment. Additionally, the system described in Mancuso requires additional space around the skimming area which in many instances may not be readily available, thus limiting the applicability of the Mancuso system.
The bubbler pipe and the skimming paddle are both consumables used during the steelmaking process, requiring regular replacement as they become damaged by repeated exposures to the hot molten metal. Thus having both a bubbler and a paddle increases production costs, further deterring steelmakers from investing in the bubbler system, despite increased yield and efficiency in slag removal. Steelmaking is a highly competitive industry, and unfortunately better systems such as Mancuso's are unattractive due to increased cost and space requirement. Thus many steelmaking mills lack a bubbler system, and rely only on the skimming process despite being less efficient. Skimmers are mainly used in the process of making iron, but can be utilized for other skimming processes involving molten metal.
What is needed is an improved skimmer that removes slag more efficiently and improves yield, all at a lower the cost for steelmakers as well as requiring no additional space.
What is also needed is an improved method of removing slag using the improved skimmer.